The subject invention is directed toward the art of pipe joints and couplings, and, more particularly, to an improved tube coupling. The coupling of the invention is especially suited for use in ultra-high vacuum applications and will be described with particular reference thereto; however, as will become apparent, the invention is capable of broader application and could be used in other systems and under a variety of different pressure conditions.
U.S. Pat. No. 3,521,910 to Callahan, et al. discloses a tube coupling which is in widespread use in both pressure and vacuum systems. However, it has achieved particular success in ultra-high vacuum applications.
The coupling disclosed in the noted patent is comprised of first and second coupling components having a generally annular configuration with an axial through passage and end faces perpendicular to the axis of the passages. Sealing surfaces are formed on the end faces and typically comprise an annular rib or protrusion which extends outwardly from the end face circumferentially of the passage. Generally, a flat, smooth metal gasket is positioned between the opposed end faces and threaded coupling nuts act to drive the coupling components together on opposite sides of the sealing gasket to produce a seal between the ribs and the gasket. During make-up of the coupling, it is desirable that there be no relative rotation or twisting between the cooperating coupling components and the sealing washer. Preferably, any relative motion should be suppressed or eliminated to avoid the possibility of scoring or galling of the end faces or the sealing washer. If such galling or scoring occurs, the effectiveness of the joint is significantly reduced and leaks can develop. Moreover, the ability to re-make the joint after disassembly can be lost.
In the prior art, it has been proposed that an anti-friction thrust bearing be installed between the coupling nut and the associated coupling component. The use of the anti-friction bearing tends to prevent the undesirable relative rotation by reducing torque transmission from the coupling nut to one or the other of the coupling components. Both standard and special ball and needle type thrust bearing assemblies have been used for this purpose. While this approach has been somewhat successful, it is not fully satisfactory in that it significantly increases the cost and complexity of the coupling assemblies. In addition, the use of the anti-friction thrust bearings increases the length and diameter of the coupling assemblies. Consequently, as can be seen, there exists an on-going need for a coupling design which can prevent relative rotary motion between the sealing faces of the coupling components and/or between the coupling components and the seal ring during fitting make-up.